1. Field of the Invention
This invention relates to a method for the continuous filtration of fluids, and especially for the cleaning of fluids such as drain water or the like. In the method of the invention, there is used a filter bed consisting of a particulate material, such as sand. The particulate material is moved downwardly in an upright-standing cylindrical annular container that is bounded by fluid-permeable walls, and is circulated, being withdrawn from the bottom, regenerated, and returned to the top. In the method of the invention, the liquid to be filtered is led into the inner part of the annular container bounded by the fluid-permeable walls, and it is led transversely to the movement of the filter bed throughout its entire height. The invention further relates to the apparatus for performing the method of the invention.
2. Description of the prior art
The methods and apparatus hitherto known or used for the continuous filtering of fluids are, on various grounds, not satisfactory.
An ideal plant for a continuous filtration process requires, among other things, an uninterrupted introduction of the liquid to be filtered into the filter bed. With the known apparatus, the introduction is usually performed through fluid-permeable walls such as jalousies, sieve grids, or the like, which become plugged relatively rapidly.
There is also known an apparatus, one in which good cleaning is obtained by the introduction of a step of microfiltration, but in such a process, instances of plugging develop because of the flocculation of impurity particles in the liquid to be filtered.
Ideally, in a continuous filtration process, the bed consisting of particulate filter-media particles also flows regularly. In the processes hitherto known, however, there are often developed irregularities in the flow movement filter-media particles which lead to the development of preferred flow streams, or narrow areas can form an unwanted bridge, which likewise leads to unwanted blockages in the filtering operation. To obtain a flow of particulate filtermedia particles as regular as possible, it is known to use apparatus that contains in the region of the flow paths at various places a number of radial guide vanes, with the use of which a certain degree of improvement is obtained. Nevertheless, even with the use of such measures, irregularities occur in the movement of the filter particles and the filtering action is less than ideal.
In connection with methods and apparatus of the type indicated above, it is also already known that it is advantageous to produce a vortex or whirling bed in a lower conical part of the apparatus, a part from which the particulate filter-media particles are withdrawn and led away to the upper side of the filter bed for regeneration. This can be done, in a manner already known per se, by the introduction of water into the conical part.
For drawing off the particulate-media particles, there has been regularly used a mammoth pump (compressed-air lifting device) of a kind which is already known per se. In accordance with known practices, the air pressure for this pump has been supplied steadily, rather then in pulses.